The present invention concerns improvements in weft feeders for fluid jet looms. More precisely, the object of the invention is to automatically restore in such feeders the continuity of the weft yarn from the spool to the loom, in case of yarn breakage or interruption.
As known to the skilled in the art, in a fluid jet loom (particularly an air loom) the arrangement usually adopted for weft yarn feeding is that shown in the diagram of FIG. 1 of the accompanying drawings. The weft yarn 4 is drawn from a stationary spool or reel 1--through one or more guide eyelets--by the weft feeder 2. It is also known that said feeder essentially comprises an electric motor 5, which causes the rotation of a winding arm 6, and a drum 8, held stationary, onto which the arm 6 winds up the yarn into even turns, forming a certain amount of weft yarn reserve detected by sensors 7. The main loom nozzle 3, provided to launch the weft yarn into the warp shed, draws from the drum 8 of the feeder 2 the weft yarn length required for each weft insertion, which length is measured by the feeder counting the number of unwound turns, for instance by means of photoelectric cells 9. One or more electromagnetic stopping devices 19 block in known manner the yarn 4 on the drum of the weft feeder 2, stopping loom feed, as soon as the weft yarn let out from the weft feeder and launched into the shed has reached the predetermined length.
The absence of weft yarn, due to running out of the spool or reel 1, or to yarn breakage somewhere along its path, is detected and signalled by suitably positioned sensors, as 7 and 9.
Weft yarn interruption generally requires the intervention of an operator, so that the yarn may be recovered from the reel 1 and introduced by hand into the various guide members, as far as the main loom nozzle 3; it is a rather long and tiresome operation, having to be carried out while the loom is not working, with consequences from the productive point of view which need not be illustrated. It is therefore evident that loom users are highly interested in disposing of systems allowing the automatic insertion and/or re-insertion of the weft yarn in loom feeding.
The designers of weft feeders have long been faced with this problem, which is at present most felt.
It should be said that there are already known to be various methods and devices allowing to reach this object by using mechanical or pneumatic means (those described in EP-0 216 220 are cited as a general example), but all such devices are quite complicated, fairly bulky and subject to the risk of faults.
Systems have also been proposed, which provide for a change of the reel and for the use of a knotter, as in EP-0 269 140; but this system is able to repair the interruption only if it occurs upstream of the weft feeder, or as the yarn reaches the weft feeder drum; furthermore, due to the difficulty in finding the broken yarn end and pulling it correctly to the side of the new yarn end, the knot sometimes fails to tie or often does not turn out well, which can cause further faults in the fabric being woven on the loom. It is thus evident that the problem needs to be solved with simpler and far safer means, which should moreover be integrated as far as possible with the feeder itself.